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Here there be monsters.

Since ancient times, some cultures have had a superstitious fear of the ocean. It was vast and almost completely unknown. It could smash any ship man dared float on it, or sweep it away, never to be heard of again. Oh, and there may have been gigantic monsters in it. Until recent centuries many sea charts were illustrated with mythical and fearsome sea-creatures in unexplored regions, and even today the weirdest creatures on Earth are to be found beneath the waves, and we're still finding more. Some of them are pretty enormous, too (though they're not the most dangerous things down there).

There are many flavours of Sea Monster (well, yes, most taste a lot like squid, unsurprisingly). These subtropes include:

  • Fiendish Fish
    Huge, hungry fish, either supersized versions of existing species or cryptids. They taste like fish, obviously.
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  • Giant Enemy Crab
    Really big crabs. Well, other crustaceans, too. They all taste a lot like crab, though.
  • Giant Squid
    Really big squid. Older Than Feudalism, they have the benefit of actually existing. They would make great calamari if their flesh didn't contain so much ammonia for buoyancy.
  • Kraken and Leviathan
    The epically scaled, humongous world-ending dwellers of the deepest trenches, often with lots of references to Lovecraftian or Biblical beasts. Tastes like whale meat.
  • Megalodon
    This prehistoric beast is great for those who like to buy their shark fin soup in economy scale.
  • Monster Whale
    Ravenous, ship-smashing and sailor-swallowing cetaceans born out of early man's dim understanding of the sea's largest denizens. They taste a lot like wild game, but are very fatty.
  • Monstrous Seal
    When they're not cute, seals tend to be portrayed as heartless killers. They mainly target penguins, but may attack humans as well. Supposed to have very lean meat, with a gamey, iron-y taste almost like organ meat.
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  • Sea Serpents
    Giant snakelike beasts who enjoy crushing ships in their coils. Very bony, with a fishy aftertaste.
  • Stock Ness Monster
    Those that ape (or more like serpent) the queen of cryptozoology, her royal slitherness the Loch Ness Monster. Said to taste rather exotic, like crocodile meat.
  • Turtle Island
    Those whose large size combined with a sedentary life in shallower conditions make them liable to be confused for islands. Apparently the taste of giant turtle is meant to be better than any chicken, beef, mutton or butter and a favourite for long sea voyages.

Please place examples belonging to those subtropes only in the specific page, not here.

See also Fish People, Our Mermaids Are Different, Space Whale, Giant Flyer, Threatening Shark, Tentacled Terror, Kaiju and Our Cryptids Are More Mysterious.


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  • A series of Jameson Irish whiskey commercials feature John Jameson jumping overboard to retrieve a barrel of booze. A giant octopus is seen reaching towards him underwater in some versions. Viewable here.

    Anime & Manga 
  • Digimon has an entire group of digimon devoted to this in the form of the Deep Savers. Of particular note are the Seadramon family, which includes the season one baddie MetalSeadramon, and the enormous Demon Lord Leviamon.
  • Fushigi Yuugi gives us Seiryuu. In his beast form, he is a dragon with water-based powers.
  • In Made in Abyss, the subterranean Sea of Corpses apparently plays host to a few. Only one is ever seen, an enormous thing that looks like a much larger version of an angler fish. How dangerous it is or how many there are isn't known, since swimming in the sea is usually a one-way trip for different reasons, but it looks more dangerous than anything encountered up to that point.
  • Magical Girl Lyrical Nanoha A's: One of the magical creatures from which the Wolkenritter took Mana was a many-eyed giant sea monster that emerged from a whirlpool.
  • Mazinger Z: The Dragonosaurus from a Crossover movie featuring characters and Humongous Mecha from Mazinger Z, Great Mazinger, UFO Robo Grendizer and Getter Robo was a real weird, gigangic sea monster. Its body was a gelatinous, amorphous blob with a face on it, and several snake-like heads sprouted from it. It was told it was a — formerly believed extinct — prehistoric monster had mutated cause oil spills polluting the ocean.
  • Miss Kobayashi's Dragon Maid: Elma's true form is a massive one-horned sea serpent with a trident shaped tail.
  • Naruto:
    • The Three-Tails and Eight-Tails, a giant turtle-crab creature with water-based powers and an ox-like kraken monster, respectively.
    • There's also a giant squid that was the guardian of an island where Killer B and A trained.
  • One Piece, being a pirate-themed adventure, has lots of sea monsters — the Sea Kings being a pretty prevalent example. They, along with a lack of winds, make it nearly impossible to enter the Grand Line from anywhere but the entrance. To put an image in mind, Sea Kings can rival islands in size and usually attack whatever they see.
  • Pokémon: In one episode, Team Rocket accidentally created a giant Tentacruel, with what they believed was a poison. Misty had to convince it not to destroy a city.
  • Sgt. Frog: One episode has several sea creatures crawl out of the ingredients pot and come in contact with the Flash Spoon, which turns them into giant sea creatures.
  • The monster in Junji Ito's "The Thing that Drifted Ashore" looks like a combination of an eel, a mass of barnacles, and the nightmares of everyone in the world who suffers from thalassophobia. It's implied to be far from the worst thing out there.

  • The Carta Marina of 1539 depicts a sea-serpent, numerous types of gigantic whales, a merman, a marine unicorn, a sea-cow, a kind of giant seahorse, a giant lobster holding a man in his claws, a bizarre "sea-hog", a so-called "sea monk" and various other weird fishes or sea creatures.

    Asian Animation 
  • Happy Heroes: Episode 24 has the heroes go to a beach to find a sea monster that is said to live there. They never find an actual sea monster, but they, along with the beach's other visitors, mistake a costume being used by Big M. and Little M. for one. As it turns out, the idea of a sea monster living at that beach was what was bringing people to it in the first place, and defeating the fake "monster" doesn't bode well with the visitors.

    Card Games 
  • Magic: The Gathering has tons of sea monsters. Leviathans, krakens, sea serpents, Giant Enemy Crabs, assorted giant fish and whales... notably enough, they're often blue, absurdly huge and little more than ravening predators, despite the Blue color being anything but based on brute force. Of note is the Serpent-typed Sea Monster card.
    It's easy to believe the monster is a myth—until you feel three hundred thousand pounds of myth crashing down on your ship.
  • Yu-Gi-Oh! features many sea monster cards. Most notably are Sea Serpents which are a whole monster type, and many Water monsters can count.

    Comic Books 
  • Fantastic Four: Giganto/Monstro, the Sub-Mariner's giant whale with arms and legs.
  • Last Days of the Justice Society: The Midgard Serpent, which Johnny Thunder and Green Lantern fight to the death.
  • Superman mini-series The Krypton Chronicles has Pryligu, a green-scaled reptilian monster whose jaws are large enough to snap a ship into half.
  • The Sandman: A sea serpent appears in the story "Hob's Leviathan", part of the "World's End" arc.
  • The Trigan Empire: The oceans of Elekton are filled with monsters.
  • The Warlord: The oceans of Skataris are filled with monsters.
  • Wonder Woman Vol 1:
    • The Golden Age/Earth-Two: Amusingly the ocean around Queen Clea's Atlantean principality is filled with monsters that resemble flying dinosaurs more than any sea creature. Diana also fights gaint flying fish with tentacles when she faces the Neptunians.
    • The Silver Age/Earth-One: Wonder Girl fights a giant sea spider that had caught her merboy friend Ronno in its web.

    Fan Works 
  • Aska has the Jormungand itself.
  • Children of an Elder God: In chapter 4 Asuka fought Amaliel, an aquatic, sea-dwelling monster resembling a viscous blob with tentacles and pincers.
    " almost globular torso, with six long sinuous limbs terminating in crab-like claws. From the upper end a subsidiary globe bulged forward bubble-like; its triangle of three staring, fishy eyes, its foot-long and evidently flexible proboscis, and a distended lateral system analogous to gills, suggested that it was a head."
  • Embers: Man-eating Seahorse dragons, leeches that can give hell to the Unagi, and (by chapter 43) something huge that makes Sokka think twice about pentapi. All stem from the Ocean Spirit's ongoing revenge, and they probably aren't the only things that we'll see.
    • Add to that list the Isonade, or shark monster, that Azula faced as she was battling with Makoto.
    • Walking Whales, a.k.a. the Kadzait. They can grow to huge sizes (the skeleton Zuko encounters is 50 ft. tall), live extremely long lives, and can be good or evil, just like dragons. The Dark ones are known as sea serpents. In Chapter 78, Zuko defeats a sea serpent banished from his clan for cannibalism of the pods' children.
  • Embers In The Dark: The oceans of Avernus are full of them. Notable examples are Krakens, Island Turtles and the Deep Ones.
  • Fallout: Equestria - Empty Quiver: Page 53 reveals rather large one, large enough to punch foot long holes through armoured bulkheads just by casually passing over them, is lurking just off shore. The monster is later revealed to be a kaiju-sized Anglerpony, easily big enough to dwarf most buildings and swallow a pony whole. However, the battle itself is something of a subversion of the usual tropes. While still extremely frantic and terrifying, the monster's size works against it, making several obvious vulnerabilities all the easier to hit and severely slowing its speed. This allows it to be brought down in half a chapter thanks to a sustained barrage from multiple tanks.
  • It's not the Raptor DNA: Lilly the Mosasaurus, as in the movies. This really comes into place when Owen is forced to swim into the lagoon to rescue the as-of unidentified man, and he imagines Lowery to be playing the Jaws theme in the control room.
  • The Keys Stand Alone: The Soft World: Part of the massive danger of the Hungry Sea (as if crazy-making waters and instant thunderstorms weren't enough) is the presence of large and hungry sea monsters.
  • One World: Quite a number appear in the story, ranging from the dragon-like Knucker to the mythical Kraken of the north sea.
    • Giant Squid: Obviously, there's been one at Hogwarts since the very first book.
    • Kraken and Leviathan: A Kraken attack is blamed for the disappearance and death of Bernard Gibbon and his squib partner. In reality, they are killed in a firefight with MI-5 Agent Kim Hunter.
  • The Palaververse: Numerous sea monsters are known to lurk in Theia’s oceans, including carnivorous whale sharks, angel sharks capable of temporary flight, and schools of skeletal bonefish. The deepest, most chaotic abysses beneath the Burning Mountains and the Black Ocean host even stranger things, from colonies of literal spider crabs that spin webs across ocean trenches to Lovecraftian horrors to wild metal-eating Smoozes.

  • The Beast from 20,000 Fathoms, a giant dinosaur-like monster that emerged from the sea after thawing out of an iceberg.
  • Deep Rising: Features man-engulfing tentacles that act as though they are independent creatures but are, in fact, attached to one giant mutated cephalopod.
  • DeepStar Six is primarily about a deep sea construction facility's struggles with an unidentified, armour-plated sea monster, with no perfectly clear analogs to any known sea life.
  • Godzilla and related films:
  • Jaws and its host of imitators popularized a combination of this trope and the Threatening Shark in cinema, presenting the largest extant carnivorous shark species, the Great White, as a man-eating monster.
  • Jurassic World: The various prehistoric creatures exhibited in the park include a much-larger-than-Real Life Mosasaurus — one large enough to surge onto shore to drag a very large predatory dinosaur to a water grave, in fact.
  • Pacific Rim: The Kaiju , which emerge from a rift in the middle of the Pacific and swim towards major human cities. The last batch that guard the Rift in particular seem specifically designed for underwater combat.
  • The Phantom Menace: There's Always a Bigger Fish in the Abyss, the watery core of Naboo. First, there's the Opee Sea Killer, a bizarre fish-crab hybrid that catches prey with a long, sticky tongue. Then, there's the larger Colo Claw Fish, a giant sea serpent with clawlike appendages used to capture smaller creatures (including baby Sea Killers, which can however chew out of a Claw Fish's stomach to escape). And finally, there's the Sando Aqua Monster, resembling a cross between an otter and a newt, but far bigger than the largest whales and the biggest predator on Naboo, who can and will eat almost anything (including the aforementioned Colo and Opee) that stands in its way.
  • Sea Monsters: A Prehistoric Adventure is a 2007 National Geographic movie about the various terrors of the Late Cretaceous seas.
  • Ultraman Cosmos 2: The Blue Planet: The Reijas are a benevolent, non-hostile example, being protectors of the oceans' depths who prefers spending their time alone underwater. When Earth gets invaded by the Scorpiss legion, several Reijas shows up on the surface to help defend the Earth.

  • The California Voodoo Game: In the massive live-action RPG tournament , the aliens responsible for all the weird events were stranded on Earth because they'd grown into adulthood since their ship crashed. Their mature forms were those of massive flatfishes more than 50' long, so they could no longer fit into their spaceship. Too bad the players never made it back up to the roof, to sneak a peek at the swimming pool...
  • Chronicles of the Emerged World:
    • The sanctuary in the Land of the Sea is guarded by a tentacled, multiheaded monster resembling Scylla.
    • The way to the Submerged World is guarded by a marine monstrosity so vast that the crew of the Black Demon doesn't even notice it at first — when they run aground on its flesh, their first thought is that the water has turned unusually thick somehow. The creature itself, from what can be seen, resembles a titanic polyp and hunts by waiting for ships or creatures to become stranded its flesh, at which point its pulls them towards its maw with ripples of its flesh and a veritable forest of tentacles.
  • Cthulhu Mythos: In H. P. Lovecraft's short story Dagon, the protagonist is traumatized by the sighting of a large, unidentified sea creature. In this case the creature itself never actually does anything particularly hostile, it's just the complete unfamiliarity with this being that freaks him out. Lovecraft also wrote the better-known Cthulhu, who would also qualify although he isn't necessarily confined to the sea.
  • Destroyermen takes this trope to an insane level. In this alternate world, the great white shark is a small predator with loch ness style creatures being average size and everything being dwarfed by the monster fish, a sea creature so ridiculously enormous that it could swallow an aircraft carrier in one bite.
  • Discworld: The illustrated novel The Last Hero features a map of the disk with all sorts of monstrous sea creatures popping up here and there. Then a later illustration shows Mustrum Ridcully fishing... with all those creatures lying in a pile at his feet. Turns out the creatures on the map weren't quite on scale.
  • Dora Wilk Series: In one of the short stories, Eryk is attacked by some sort of sea serpent which crossed over from its plane into our reality. Szelma has to rescue him.
  • Galaxy of Fear: In The Nightmare Machine, the heroes visit Hologram Fun World and interact with a simulation of a whaladon, which is friendly at first but later tries to get them.
  • Journey to the Center of the Earth: While crossing the Lidenbrock Sea, the characters witness a furious battle between an Ichthyosaurus and a Plesiosaurus portrayed more or less accurately for the time, meaning as gigantic and savage monsters.
  • Liveship Traders: Sea serpents feature prominently, as they're the larval stage of dragons.
  • Lord of the Flies also has the whole "beast from sea" speculation affair.
  • The Lord of the Rings: The Watcher in the Water appears to be something like a giant octopus.
  • In Orlando Furioso, two different women, Angelica and Olympia, were offered to placate two different sea monsters — at least one of which was called an orc. Also, the enchantress Alcina uses a whale as transport.
  • Percy Jackson and the Olympians:
    • Percy Jackson encounters the legendary Charybdis and Scylla in The Sea of Monsters, a random sea serpent in the short story Percy Jackson and the Stolen Chariot from The Demigods Files, and sees a whole army of them attack Poisden's forces in The Last Olympian.
    • The sequel series has the main group encounter Ceto, the mother of all sea monsters (though she certainly doesn't look like one when she shows up), and one of her children, the Skolopendra, which resembles a monstrous seagoing cross between a worm and a centipede.
  • The Scar: The Avanc (from the afanc of Welsh mythology), an absolutely colossal monster hailing from an extradimensional ocean, large enough to pull the floating city of Armada behind it as it swims.
  • Sense and Sensibility and Sea Monsters, which is essentially Sense and Sensibility, except everything in the ocean developed a psychotic hatred of mankind.
  • The Traitor Son Cycle: The Eeeague are some sort of tentacled, fairly intelligent creatures that roam the North Cross Ocean. One of them is enough to sink a ship.
  • The Voyage of the Dawn Treader: On its journey east, the Dawn Treader comes under attack from a sea serpent.
  • The Witchlands has sea foxes, which are giant, carnivorous sea serpents with heads of foxes. They're attracted to the scent of blood in the water and can crush ships in pursuit of their prey. Most people consider them mythical, but Safi, Iseult and Merik encounter — and are nearly killed by — two of them when they're sailing to Lejna.
  • The Xandri Corelel novel Tone of Voice has giant predators known as Disharmonies. They attack in packs and can easily take down Voices or ships.

    Live-Action TV 
  • Mighty Morphin' Power Rangers: The Dragonzord is this in robotic form, rising dramatically from the ocean to wreak destruction upon either the city of Angel Grove, or the forces of evil, depending on who possesses the Dragon Dagger, and whether the rightful owner of the dagger is in control of himself. It is a Godzilla-esque metal beast, and of endurance as yet unmatched.
  • Primeval has featured a few prehistoric sea monsters. Episode 1.3 gave us a Mosasaur, Episode 2.4 gave us a future shark and the Mer, walrus-like sea monsters that appeared to have evolved from primates, and Episode 5.2 gave us a whole pack of Pliosaurs.
  • The miniseries Sea Monsters (from the creators of Walking with Dinosaurs) features some of the nastiest aquatic predators that ever existed in Real Life.
  • Ultra Series: Since the Trope Codifier of all Japanese kaiju was a Sea Monster, the Ultra Series has lots of marine kaiju. Examples include:
    • Gubira of the original Ultraman is a giant narwhal-like beast with a drill for a horn who goes by the subtitle "Deep Sea Monster". The giant lizard Gesura, the two-bodied bat-starfish Pestar, and the whale-toad Gamakujira would also count.
    • Eleking from Ultraseven is a Psycho Electric Eel kaiju, who, while appearing in a lake in his original series, has appeared in the ocean in other shows. Seven also battled a monster called Guyros, a giant mass of octopus tentacles controlled by the mysterious Nonmalts, while Iron Rocks, a monstrous robot built by aliens from the remains of WW2-era submarines and warships could also be considered one.
    • The first episode of Return of Ultraman features a battle between two sea monsters, the sponge-based Takkong and the seaweed-like Zazahn. Later on Ultraman Jack would have to battle several others, including a mated pair of weather-controlling monsters called Seamons and Seagorath, the jellyfish-like Varricane, and the fish-dinosaur mix Muruchi.
    • Angoras from Ultraman 80 is a giant anglerfish monster who absolutely towers over the Ultra. But it turns out to be a Non-Malicious Monster who is only seeking it's missing child who was caught by humans; upon the baby Angoras being released into the lake it was from, the adult promptly leaves and never returns.
    • Leilons from Ultraman Tiga is a Friendly, Playful Dolphin turned into a kaiju by nuclear waste leaking into the ocean. Despite now being a giant monster, he still maintains his Friendly and Playful personality, even when battling Tiga.
    • Ultraman Dyna battles a sea serpent named Dipras in one episode. Later on, he faces off the aquatic bigger-than-Ultraman alien Spume and its crab-like enforcer Reicubas.
    • Ultraman Gaia''s Bokurag is a crab-fish-lizard mix made partially out of water, meaning it's effectively invisible to XIG's monster-detection technology whenever it swims.
    • Ultraman Max' has Flygler, a mutated flying monster based on flying fish. It can fly as fast as it swims.
    • Ultraman Mebius' Arigera is an eyeless pterodactyl-like kaiju that can glide through seas and skies alike at supersonic speed.
    • Maga-Jappa from Ultraman Orb is the King Demon Beast of Water. While the characters actually encounter him at a lake, his seahorse-like appearance and ability to render water foul-smelling with his presence suggests he's mainly an ocean monster.
  • Walking with Beasts': The Basilosaurus'' is a giant predatory whale big enough to devour nearly anything else it encounters in the water.
  • Walking with Dinosaurs: The Liopleurodon in "Cruel Sea", besides being notably oversized compared to its real-life dimensions, is portrayed as a terrifying, relentless predator ruling over the seas and devouring anything that catches its attention. A Plesiopleurodon cameos briefly in "Giant of the Skies", serving as a reminder of why the Ornithocheirus should cross the Atlantic fast and without getting close to the water.

  • Asia: A sea monster appears on the cover of the 1982 self-titled debut album.
  • Voltaire: The Beast of Pirate's Bay from the song of the same name, which supposedly has a habit of eating careless sailors. The last verses reveal that it's just a legend that the narrator himself made up, to keep people from disturbing a wounded whale hiding from hunters in Pirate's Bay.

    Mythology & Legend 
  • Older Than Feudalism: Charybdis, from The Odyssey, an unseen monster that swallows and spits out the entire ocean on a regular basis in the form of a giant whirlpool. Related is Scylla, who lives near the ocean rather than in it and has lots of heads note 
    • There was also the skolopendra, a sea monster resembling a giant, 200ft prawn with a mass of tentacles coming out of its face.
  • Another even older Older Than Dirt example: Tiamat, the primordial sea serpent from the Babylonian creation myth Enûma Eliš.
  • Many a woman Chained to a Rock was to appease a Sea Monster. From Greek legends, Hesione and Andromeda's monsters. Andromeda's was named Cetus, which of course means "whale" now.
    • To add insult to Cetus' mortal injury, after Perseus slashed her throat, he delivered the deathblow by showing him the petrifying head of his own sister, Medusa, transforming Cetus into a coral reef.
  • The Con Rit, or Tarrasque, a sea serpent claimed to be found in the South China Sea. Some theories say that the possible sea serpent is inspiration to both the Oriental Dragon, and the South African Snake God. note 
  • The Kalevala has a giant pike and Iku-Turso, a malevolent sea monster.
  • Norse Mythology has the Kraken of course. And then there's Jormungandr, the Midgard (World) Serpent, the sea monster to end all sea monsters. An immense sea snake, he wraps all the way around Midgard, holding his tail in his own jaws. He has a major rivalry with Thor, and plays a key role in Ragnarok.
  • Icelandic folklore tells of the "illhveli", strange whales of supernatural nature and aggressive temperament. It was thought that their flesh was inedible and that they would appear if their names were spoken aloud at sea.

    Other Sites 

  • Seawitch depict two monstrous sea creatures as war mounts — one is a giant fish with fangs and ragged wings, while the other is a barracuda-like serpent.

  • Dice Funk: One pursues the party throughout Season 2, episode 3. The existence of such creatures is an important plot point. It was eventually revealed that there was only one large monster stalking the seas of Lorelei. It just happened to be a chimera of every single sea god in the multiverse.

    Professional Wrestling 

     Tabletop Games 
  • Dungeons & Dragons:
    • Sea Monsters by the truckload: scyllans, krakens, leviathans, ramfish, dragon turtles, sea drakes.
    • And then there's Dagon, a lesser-known demon prince who is an eel with the head of a freaky fish, six tentacles ending in clawed hands, and more eyes than I really want to count. Other demon princes are afraid of him.
    • The ocean-oriented Stormwrack book includes many Sea Monsters.
    • Older editions had the behemoths (giant hippos), aquatic "dinosaurs" (Elasmosaurus, Mosasaurus, Nothosaurus, Plesiosaurus), dragons (lung wang and yu lung), froghemoths, giant creatures (giant crayfish, giant crocodiles, giant octopi, giant sea snakes, giant squid, giant turtles), giant fish (afancs, giant eels giant gar, giant pikes, vermes), merrow (aquatic ogres), mottled worms (aquatic purple worms), sea serpents, seawolves (aquatic lycanthropes), and vodyanoi (aquatic umber hulks).
  • Exalted:
    • The armored terror (that's the actual in-universe name) is a thirty-foot-long carnivorous fish covered in armor-like scales and provided with a beaklike pair of fangs easily capable of severing limbs. It normally hunts fish in shallow water, but it's perfectly happy to go after boats and people. Physically, it sounds a lot like an oversized Dunkleosteus.
    • Benthic knifeooths are serpentine sharks up to twenty feet long. They are aggressive predators and will attack almost any prey they come across, and the mere sight of one swimming near the surface is enough to drive sailors into panic.
  • Middle-earth Role Playing : The creatures of the oceans are noted to have suffered significant corruption, more so than most other natural creatures, due to Morgoth's brief seduction of Ossë allowing him to introduce many of his monstrous creations into the sea, where they remain to the present day. Even redeemed, however, Ossë and his servants are much more tempestuous and aggressive than his wife Uinen and the natives of her freshwater domain, and even uncorrupted creatures can be dangerous to seafarers. These creatures include a variety of naturally and unnaturally aggressive fish, sharks and whales, as well as monsters such as krakens and marine dragons.
  • Monsterpocalypse has the Tritons, whose main monsters are kaiju-sized sea creatures.
  • Pathfinder: The oceans of Golarion are not friendly places, and are home to a wide assortment of dangerous monsters.
    • Numerous types of marine dragons — such as bronze dragons, sea dragons, brine dragons, dragon turtles, cetoi and sea drakes — are widespread throughout the world's seas.
    • Primordial creatures also abound, especially in seas far from civilized lands — elasmosaurs, plesiosaurs, tylosaurs, megalodons, basilosaurs, dunkleostei and camerocerases are all known.
    • Other sea monsters include the monstrous, evil krakens; enormous and feared sea serpents capable of crushing ships in their coils; wolf-headed ketesthiuses with entire ships and lesser monsters trapped in their cavernous bellies; scyllas and charybdises; whaler jellyfish; undead bakekujiras; a variety of monstrous sharks such as isonades and the three-headed, tentacled luscas; and the Leviathan itself.
  • Rifts has boatloads of sea, lake, and even river monsters.
  • Shadowrun: The return of magic into the world populated the oceans with a fair assortment of giant, seagoing monsters.
    • Leviathans are immense whales descended from orcas, and some of the largest creatures in the ocean.
    • Leviathan dragons are immense, ocean-dwelling relatives of the three land-bound variants, and like them grow to be nearly unkillable forces of nature.
    • Megalodons are giant sharks descended from great whites, and will attack and try to eat anything they encounter.
    • Seadrakons are mosasaur-like sea reptiles the size of a whale, and will happily attack cetaceans and human boats.
    • Sea serpents are plesiosaur-like dragon relatives with flexible necks and ridged backs. They're aggressive predators and will attack very large prey, including whales and seadrakons.
  • The Warhammer world has buckets of these, as detailed in several places.
    • The Seas of Blood supplement to the early 90s naval warfare spin-off Man O War includes the classic giant squid Kraken and the horrific Black Leviathan (a humongous deep-sea angler fish that can swallow small ships whole), as well as the Narwhal-like Behemoth, the giant crab Promethean the Sea Dragon, the giant merman Triton, the Sea Elemental and the giant shark Megalodon.
    • Dreadfleet, another spinoff centered on naval combat, has several zombie sea monsters — the Sea Giant, Bone Hydra and Leechwyrm — and even a ship made from the rotting undead carcass of an Orb Leviathan (possibly the same species as Man'O'War's Black Leviathan, maybe not).
    • Smaller, but still huge, sea monsters are available from Forge World to use in land-based Warhammer armies in the shape of seagoing, wingless dragons such as the Merwyrm and its variants, and the Dark Elf army has access to aquatic Hydras, Sea Dragons and the Kharybdis, a species of many-headed sea monsters native to the churning oceans around the Dark Elf homeland.
  • Warhammer 40,000 has a few, though they're rather obscure. Given the nature of the setting, it's a safe bet that most world with any oceans have at least one.
    • The Space Wolf homeworld has a massive kraken (said to be a Tyranid offshoot) and sea serpents straight out of Norse myth, appropriate given the Space Wolves' Viking theme, and a sea monster is said to live on the planet Armageddon, where it attacked Ork ships.
    • The Iron Snakes chapter has a mostly ocean-bound home world (their fortress-monastery is on one of the moons), and one of the challenges which aspirants wishing to join the chapter have to face is single combat with a sea serpent using only a harpoon and a canoe.
  • Werewolf: The Forsaken: Very old, very successful Ukusguaku — parasitic, lamprey-like spirit-beasts — are called "wyrms" because they become truly enormous lampreys with disturbingly human eyes.


     Video Games 
  • Aquanauts Holiday has several whales swimming in its oceans, but there's also an enormous prehistoric fish floating in the southwest corner of the map.
  • Arcana Heart: Niptra, an ancient fish that became the largest and wisest fish in the seas through cycles of reincarnation before finally becoming the Arcana of Water.
  • ARK: Survival Evolved: Being a game about surviving on an island full of dinosaurs and other prehistoric animals, naturally the waters of the game world are also full of aquatic beasts. These range from the rather friendly Ichthyosaurs and common-to-the-point-of-being-mundane Megalodon that can be found almost anywhere in the ocean to much more exotic marine reptiles like Mosasaurs and Plesiosaurs, and a Cretaceous giant squid called Tusoteuthis which lives only in the farthest depths. If you're determined enough and have the right equipment, you can tame these sea monsters and put them to good use.
  • Azada: Ancient Magic: One of the later puzzles requires you to free the Baron (Munchausen) from a giant sea monster's mouth.
  • Banjo-Kazooie:
    • The boss of the obligatory underwater level in Banjo-Tooie is Lord Woo Fak Fak, a gigantic lanternfish who literally lives in Davey Jones' Locker. He can be a bit tricky, but is much easier to fight if you use the Submarine transformation.
    • In Jolly Roger's Lagoon is a giant fish that swallowed Merry Maggie the barmaid. Strangely, it doesn't try to attack you, even when you knock all the teeth out of its mouth in order to rescue her.
  • Bayonetta:
    • Sapientia is a massive angelic being that resembles a crocodile of sorts and has powers over water. You fight him out in the middle of the ocean, where at one point he even dives below and reaches up from under water.
    • Bayonetta 2 introduces a species of demons known as Insidious, resembling giant roboticnote  manta rays that house several smaller demons inside of them. While they can fly and be found anywhere, the first one is encountered in a massive underground lake, and fought as an underwater battle.
  • Big Ol' Bass 2: This is the entire point of the World Monster Fishing mode. You can catch everything from bass with the American flag colors to a trout with the Mona Lisa on it to a shark with a leopard design to dinosaurs.
  • Cobra Triangle featured several different sea monsters to include a Giant Enemy Crab, a Giant Squid, sea serpents and giant shark as the final boss.
  • Dark Cloud 2: The Shiguras, extremely reminiscent of Pokémon's Lapras. Dr. Jaming intends to use them as tools for his own nefarious purposes, and goes as far as to enslave one of them, Pau's friend, Shingala.
  • Dwarf Fortress:
    • Sea monsters are a specific kind of creature that spawn in evil oceans (any biome can be good, neutral or evil in-game). As the game is text-based they don't have a visible appearance, but the game describes them as having multiple eyes and arms, as well as two pincers. They're fearsome enough in the sea, but cannot move if stranded on land. When dwarves like them, they do so for "their horrifying freakish appearance".
    • There are also Sea Serpents, which resemble limbless dragons and can spawn in any savage ocean.
    • Savage oceans are also home to Giant Squid, giant octopi, giant cuttlefish, giant orcas and giant sperm whales (the latter of which grow to be the biggest things in the game, bar none), all of which are more than capable of killing your dwarves by the dozens.
  • Earthbound gives us the Kraken, a fire-breathing sea serpent. It's considered The Dreaded of Summers, and for good reason.
  • The Elder Scrolls IV: Oblivion has the Giant Slaughterfish.
  • Endless Ocean: Blue World features several prehistoric creatures to be encountered, one of whom even tries to attack you. There's also lots of benign marine life which have monster-esque names, such as a giant squid named "Kraken Jr." (still technically an infant, but one that will eventually grow into a full-scale sea monster) and an albino sperm whale named "Leviathan". Sadly, all of the prehistoric creatures are relegated to cutscenes only and cannot be swam with.
  • Final Fantasy: Kraken herself shows up as a boss in a few games. Final Fantasy X also features a few since your characters are now able to fight underwater. Geosgaeno who is one of the first fiends you fight definitely qualifies — he's a Bonus Boss later in the game. The Giant Flyer Evrae turns into this the second time you fight him, though he's also a zombie. There's also a couple of Sinspawn fiends that you have to fight underwater.
  • The God of War series loves this trope. But again, the games are based on Classical Mythology:
    • The Hydra from the very first game and the very first boss. It is a serpent with lots of heads just like in Classical Mythology, the games are based on.
    • The Kraken in the second game. He looks similar to how he looked like in the Clash of the Titans but with classical elements thrown into the mix as well.
    • Hippocampi, the water creatures of Poseidon, in God of War III.
    • Scylla in Ghost of Sparta looks like a hybrid of different sea creatures, including a shark, a squid, a crab and a narwhal.
  • Grim Fandango: In the third chapter, Manny ends up on the bottom of the ocean, which is pitch black except for a single light source. Upon finding another traveler, trying to walk to the other side of the ocean (and failing at it by walking in circles for years), Manny gives him a warning.
    Manny: Watch out for sea monsters.
    Chepito: Oh, these guys?
    Chepito shines his lamp at the ocean, revealing wall-to-wall, creepy-looking sea monsters just behind the darkness. The darkness you are walking through. Try not to think about that during your remaining time under the ocean.
  • La-Mulana is maybe the only video game to use the Babylonian interpretation of Tiamat (fierce ocean goddess) rather than the Dungeons & Dragons interpretation (five-headed dragon queen).
  • The Legend of Zelda: Twilight Princess: Morpheel, an eel-like fish transformed by the Twilight into a gigantic, tentacled horror with extendable jaws.
  • Metroid Fusion Serris, one of the bosses, is a sea serpent capable of Super Speed.
  • Might and Magic VI has the Sea Serpent line of monsters, giant wyrms swimming around in the Eel Infested Waters oceanic region. The second tier ones are outright named Sea Monsters (the ones in the tier above that are Sea Terrors, so named because, in addition to being one of the most dangerous non-boss creatures in the game, their attacks also inflict supernatural fear).
  • Monster Hunter: Monster Hunter Tri introduced mechanics allowing your character to swim and fight underwater. Obviously this introduced a whole slew of new aquatic monsters, including a lightning-spewing serpent/crocodile mix and a large, grotesque anglerfish capable of perfect camouflage, blinding flashes of light and inflating into a spined ball. There is also a marine Elder Dragon that is a football field long, and causes earthquakes by ramming into underwater cliffs with its horns.
  • Monster Rancher had the Zilla, a freaky whale/gorilla hybrid, and Lesione, which is a much cutesier plesiosaur-like creature with elements of trained marine mammals.
  • The Ocean Hunter has its share of giant sea creatures, the biggest of which serve as boss and mini-boss fights.
  • Ōkami: The Water Dragon, which turns out to be the king of the Dragonians.
  • Pokémon: A fairly common archetype for Water-types.
    • Kyogre, the creator and master of the seas, fills the "colossal primal sea monster" niche.
    • Gyarados is a ferocious, destructive sea serpent that can level cities, and evolves from the somewhat pathetic Magikarp. Milotic is considered its benevolent counterpart of sorts, due to the fact that it's also a serpent, it has a much calmer temperament and it evolves from an equally weak Pokemon as Gyarados, though it is much rarer. Gold/Silver/Crystal features a Red Gyarados (most are blue) rampaging in the aptly-named Lake of Rage. In the game a red Gyarados evolves from a golden Magikarp.
    • While not itself a Water-type, Lugia, known as the Diving Pokemon, resides deep within the seas of the Whirl Islands and is said to be the "guardian of the seas." It has the ability to control the weather, most notably it can calm and give rise to storms.
    • Pokémon Y has Dragalge, the Mock Kelp, a giant sea-dwelling Poison/Dragon Pokémon based on a mix of the weedy and leafy sea dragons. It's described as "vicious" and extremely territorial, hiding in kelp and attacking ships venturing into its territory. The poison it spits is strong enough to eat through the steel hull of a tanker (though in-game Steel-types still No-Sell Dragalge's poison moves).
    • Sun and Moon's Wishiwashi are, individually, very small and weak fish. However, they have the ability to school together in sync to form a giant, powerful fish-like monster still visibly composed of individual fishes. School Form Wishiwashi are very powerful, enough so to be known as the Demon of the Sea by local Alolans. Even Gyarados flee from these things!
    • Other examples includes various Giant Enemy Crabs (Kingler, Crawdaunt, Clawitzer), giant ghost jellyfish that attack ships that pass through their territory (Jellicent), a mini Loch-Ness monster thing (Lapras), a large sea-horse that whips up whirlpools by yawning (Kingdra), a vicious torpedo shark that can tear open supertankers (Sharpedo. Yeah.), numerous prehistoric sea monsters (Lileep, Anorith, Kabutops), killer crocodilians (Feraligatr), and artillery-wielding cephalopods (Octillery).
  • Resident Evil 4: Del Lago resembles some kinda giant newt.
  • Shadow of the Colossus features two: the electric eel colossus that is frankly terrifying, and the wading lake monster, which is terrifying AND frustrating.
  • In The Sims, in Neighborhood View, a sea serpent can sometimes be seen randomly at the end of the river (near Gunther Goth Highway) and swimming out into the bay.
  • Stranded Deep: There are three who serve as bosses; a Megalodon, a Giant Squid, and a giant Moray eel.
  • Subnautica, naturally. As of now, there are four "leviathan-class" creatures which are utterly enormous, and three of them are extremely hostile. There's also the reefbacks, which are so big that small ecosystems grow on their backs. There are also plenty of smaller (but still large) creatures that evoke the image of a sea monster, many of which are also happy to hunt you down if they get wind of you.
  • Sunless Sea has a lot of these living in the dark waters of the neath — giant crabs with anglerfish lures on their pincers, bound sharks and ship-sized jellyfish are some of the least terrifying things you'll run into in the Unterzee. Most of them are bigger than your ship. And then there's the Eye, which either belongs to an enormous one of these or something far, far worse.
  • Super Mario Bros.:
    • Super Mario 64 introduced Unagi the giant eel note  and the Sea Dragon — who actually lived in an underground lake. The Sea Monster's name is "Dorrie", although in Japanese it's name is "Doshi", which is a parody of the Loch Ness Monster and Yoshi since the nickname "Nessie" in Japanese is "Neshi".
    • Super Mario Sunshine had a boss named Eely-Mouth, who was more goofy-looking. Sunshine also features the fearsome Phantamanta, a massive, paper-thin manta ray that can generate electric slime capable of absorbing anything or anyone that's covered in it (Phantamanta manages to make an entire hotel vanish this way). Mario must combat the monster to save the hotel, but it's tricky, as spraying Phantamanta with water makes it split into endless smaller versions of itself, which, when it's shattered enough, start actively attacking the portly plumber.
    • Super Mario Odyssey offers Brigadier Mollusque-Lanceur III, Dauphin de Bubblaine, a giant octopus-like beast that makes himself at home on Bubblaine's famous Sparkle Water tower and starts sucking it dry.
  • Team Fortress 2: The Demoman considers the Loch Ness Monster to be his mortal enemy, and he accidentally killed his adoptive parents in an attempt to blow it up.
  • Terraria: Duke Fishron, a giant green, winged pig-thing that lurks in the Ocean biomesnote  and is summoned by fishing there with a certain kind of bait. He was also the hardest boss in the game prior to 1.3.
  • Tradewinds: Legends and Odyssey have several sea-monster battles, both bosses and random encounters. Also, in the Legends Captain's Log: "Fought kraken. Looking for good calamari recipe."
  • Almost every game in the Ultima series has one or more sea monsters. They're usually pretty powerful, and often capable of making ranged attacks, so getting too close to the coast with a low-level party can be pretty risky.
  • Wild AR Ms 4: The Sapphire Drake Bonus Boss, which the player first sees preying on another sea monster.
  • World of Warcraft: There are some rather large aquatic creatures in Azeroth's waters. Notable examples include Ghaz'rankha, a giant hydra that's a boss in Zul'gurub raid instance (gaint hydras also appear as bosses in Zul'zarrak and the Underbog), and the Lurker Below, a boss in Serpentshrine Cavern raid whose ingame model is actually called "kraken". Some of the larger naga may count for this trope too, their queen Azhara most certainly does. Hydras in World of Warcraft are lizards with three heads. They have two legs and a heavy tail, so they basically move on a tripod as well. Normal ones are about the size of a wooly mammoth or so, but bosses are a little bigger. The Lurker Below is big enough to be a genuine kraken, and three other things in the game share its same ingame model: two similar wild animals related to specific quests and a sea goddess.
  • Zoo Tycoon: Expansion packs for the original game allow you to raise and exhibit plesiosaurs and Loch Ness Monsters. Not together, though: they eat each other's eggs!


    Western Animation 
  • Avatar: The Last Airbender:
    • There's a reason that the Serpent's Pass is called such, which the characters find out firsthand when the giant sea serpent comes out when they try to cross.
    • The giant lion-turtle with an island on its back.
    • And the Unagi that lives near Kyoshi Island.
    • During the Season 1 finale, the ocean spirit assumes the form of a huge, humanoid, Godzilla-esque monstrosity.
  • Babar: "The Unsalted Sea Serpent" has a big menacing sea serpent and its baby offspring living in the local lake.
  • Beany and Cecil:
    • Cecil the Sea-Sick Sea Serpent is a benevolent example.
    • Bad guy Dishonest John had an undersea craft disguised as a giant cephalopod, known and feared far and wide as Billy the Squid.
  • Care Bears hads a sea serpent named "Shaky" who needed work on his confidence.
  • Catscratch features a Kraken, which Gordon must fight in order to wish for a longer tail.
  • Cybersix: The giant Nautilus. Cybersix beats it by dropping a bridge on it, literally.
  • The pilot of The Drinky Crow Show involves whales, which is appropriate because it's set on a whaling ship. The whales are drawn in the style of those really old maps with "Here be dragons" written in the corners.
  • DuckTales (1987): The sea monster that ate Scrooge McDuck's ice cream is actually a submarine colored to resemble an orca.
  • DuckTales (2017):
    • In the pilot episode, the cast encounter a few of them on their way to Atlantis, including a Giant Squid, a bunch of scary-looking merducks, and what appears to be a storm elemental.
    • In "The Spear of Selene!", a tentacled monster named Charybdis is guarding the temple of Ithaquack. It's a Punch-Clock Villain that protects the Spear of Poseidon and is very polite with those seeking a different artifact.
  • Kaeloo: In Episode 78, the gang, who are pirates in this episode, come across a giant sea monster which has several tentacles. For some reason, its face looks exactly like Mr. Cat's.
  • My Little Pony:
  • The Pirates Of Darkwater: Unsurprisingly, the world of Mer is full of Sea Monsters, including Darkwater itself and the huge, serpentine Leviathans.
  • Popeye and Son episode "The Sea Monster" is about Exactly What It Says on the Tin. The monster is friendly and befriends Junior.
  • Scaredy Squirrel has recurring antagonist, Sally Fishlips, A piranha-like monster complete with Scary Teeth. Nobody but Scaredy sees her as a giant monster running a muck in town.
  • Sesame Street: In an animated segment listing various small objects, a huge sea monster offers himself as an example.
    Sea Monster: I am too small. My daddy's big.
  • Spongebob Squarepants: When Spongebob yells that there are sea monsters on the beach to keep people out of the water, an erudite serpent reminds him that "we sea monsters have made great strides in the fields of science and literature."
  • In Star Wars: Clone Wars the Mon Calamari fought the separatist forces with knights riding on giant eels.
  • Star Wars: The Clone Wars: In the episode Bombad Jedi, Jar-Jar made friends with a Kwazel Maw, a giant, aquatic centipede-like beast native to Rodia. Technically a Swamp Monster, but Rodia's swamps are so wide and deep they're effectively a freshwater ocean.
  • Yellow Submarine had a Sea of Monsters.

    Real Life 
  • If one takes the vast scope of the Earth's history, many of the well-known mythological or legendary "sea monsters" do have basis in reality. Some huge water dwellers which resemble sea monsters are listed below:
    • Giant Enemy Crab — The Japanese spider crab of course, whose legspan may grow between 12 and 18 feet in total length. The creature itself weighs over 40 lbs. However, the prehistoric Jaekelopterus was far more massive, attaining lengths of up to 8 feet with and weighed possibly close to 400 lbs, though it is more sea scorpion than crab.
    • Giant Squid/KrakenExactly What It Says on the Tin — of course, the present-day GiantSquid, which can grow over 40 feet in length, as well as its larger cousin the Colossal Squid. The Giant Pacific Octopus should qualify as well, since large specimens may reach an impressive 20 feet across. Some ancient mega-cephalophods include Tusoteuthis, a 30-foot ancestor of the present-day vampire squid, and the "Giant Orthocone" Cameroceras, a cuttlefish-looking creature which resembles a cross between a squid and a snail.
    • Leviathan — Most whales largely resemble the whale-like depictions of the biblical Leviathan, though the ancient species Livyatan melvillei, named after the famous Herman Melville of Moby-Dick, deserves special mention, as it is much like the modern Sperm Whale, but with far larger 14-inch teeth. It would have been the chief (and probably the only) rival of the equally-sized giant shark, Megalodon, as both lived around the same time and the same place.
      • For depictions of the Leviathan as a great fish, we have:
      • The Whale Shark, of course, which grows from 30 to 40 feet in length with a weight of over 20 tons — almost the length of a school bus, and twice the mass.
      • The oarfish — an enormous eel-like creature which can reach lengths of 30 feet — is considerably eerier in appearance, and looks like the more sea serpent-themed depictions of the Leviathan.
      • The ancient Leedsichthys was perhaps the largest fish of all time (challenged only by Megalodon) and most updated estimates put it somewhere between 50 or 60 feet long. It looks amusingly like a supersized version of a common ray-finned fish.
      • Dunkleosteus terrelli is an extinct creature that is probably the best example (aside from sharks) which is a fish, incredibly large, and monstrous (so much so that it is hypothesized to be a cannibal to its own species). It is believed to have the strongest bite force of any vertebrate alive or extinct. It could grow up to 30 feet long.
    • Megalodon — like the giant squid, this is a straight-up real creature, albeit no longer existing (supposedly). It is hypothesized to have looked liked a Great White Shark — but around three times longer — and its famous jaw reconstructions could easily fit several people inside (not surprising for an animal whose bite could have crushed a small car). It was 50-60 feet long and weighed around 50 tons.
    • Monstrous Seal — yet another straight-up real animal. The Elephant Seal in particular is the biggest of the lot, growing 16-20 feet long and weighing 3-4,000 kilograms (that's right — an elephant seal may grow to the size of an elephant!).
    • Stock Ness Monster — the extinct Plesiosaurs, more-or-less. Additionally, they are mainly saltwater dwellers, adding to their "sea monster" image. The largest species, Elasmosaurus, could reach 46 feet in length. Other huge marine reptiles include the 69-foot Shastasaurus, the largest of the ichthyosaurs ("fish lizards"); Mosasaurus hoffmani — a terrifiying apex predator which could grow 56 feet long (the largest known lizard species of all time, essentially a gigantic aquatic Malicious Monitor Lizard); and the 49-foot Pliosaurus funkei (Predator X), also a superpredator.
    • Turtle Island — although it doesn't exactly resemble an island, the 12 foot Archelon is a candidate for the largest turtle species of all time, as well as Stupendemys, which was slightly shorter but possibly heavier.
  • And including extinct animals, we have plesiosaurs and similar creatures like the ichthyosaur and mosasaur, and Megalodon, a prehistoric shark the size of a whale. Its modern counterpart may be the Whale Shark, which is thankfully nonaggressive and feeds on plankton. Indeed, so many different creatures like this existed in the past that one can argue that plesiosaurs can't have survived to the present, because the mosasaurs would've eaten them, long before the K-T extinction took down subsequent forms of reptilian Sea Monster. The modern equivalent of Carcharocles megalodon might be the Whale Shark from a size perspective, but in every other respect it's basically a Great White that is... bigger.
  • Pliosaurus. Its teeth are each a foot long.
  • The Oarfish: an eel-like fish that can exceed fifty feet long. Harmless, but quite impressive.
  • The African country of Burundi is home to Gustave, a well-known man eating crocodile. Gustave weighs in at approximately one ton, is approximately twenty feet in length, and has been known to eat adult hippopotami. Given the number and variety of bullet-shaped scars which cover his body, it's quite possible that he's Immune to Bullets.
  • Saltwater crocodiles can be even larger than Gustave. Large adult male saltwater crocodiles can be more than six meters long and weigh more than 2,600 lbs.
  • Prehistoric crocodiles were even larger than saltwater crocodiles. Sarcosuchus imperator, Deinosuchus riograndensis and Purussaurus braziliensis were around forty feet long or longer, and all of them weighing around 7-8 tons.
    • Many of them were also fully marine. Plesiosuchus was basically an orca sized marine crocodile that looked like a shark.
  • The Bloop, or rather, whatever made the Bloop, an ultra-low frequency underwater sound that matched the profile of a living creature, but not any specific living creature we know. If it did come from a living creature, scientists agree that it would have to be several times larger than the Blue Whale, the largest known animal on earth. Interestingly enough, the signal originated from a point in the South Pacific roughly 950 nautical miles from the sunken home of another large monster.
    • Sadly, the Bloop is now thought to be the sound of an iceberg breaking up, rather than a living thing.
  • Tullimonstrum (informally called the Tully Monster), a bizarre fossil creature from the Carboniferous Period, bears a striking external resemblence to the Loch Ness Monster, except it's barely a foot long and found in North America.
  • The Coelacanth is a person-sized carnivorous fish that has been swimming around virtually unchanged for millions and millions of years. It was thought to have been extinct until live specimens were caught in the 20th century.
  • The whole point of fishing shows like River Monsters, Hooked, and Monster Fish. Their catches range from the modest (Taimen), to the bizzare (catfishes of the Amazon), to the truly gargantuan in scale (marlins, giant catfishes, and the Mekong Giant Stingray).
  • The basking shark, second-largest living fish, can grow up to thirty-plus feet. They also look rather monstrous, cruising through the water with their three-foot mouths. Fortunately for all mankind, they and whale sharks eat only plankton. They are also the source of a few sea monster myths, where the decomposing bodies of these sharks after having beached or caught as by-catch have been mistaken for plesiosaurs.
  • Sperm whales and giant squids are among the most famous modern day examples. They even engage in Behemoth Battles!
  • Several deep-sea species of shark are also quite large. The megamouth shark grows to eighteen feet in length, and the Pacific sleeper shark can grow to fourteen, though ichthyologists theorize they may grow as long as twenty-three feet. Related to the Pacific sleeper is the Greenland shark. It lives in Greenland and closer to the surface, routinely grows to seventeen feet in length and has been found with parts of polar bears in their stomachs.
  • Lion's mane and Nomura's jellyfish can grow to gigantic sizes. The lion's mane can grow nearly forty feet long and the Nomura can weigh over four hundred pounds. Nomura's jellyfish have also marked off an important check on the "to-do list" of most sea monsters; sinking ships, albeit in a passive manner. "Blooms" of these jellyfish have numbered in the thousands and at least one fishing vessel has been capsized after trying to haul up a net full of these jellyfish.
  • Syringammina fragilissima. It's a deep-water denizen eight inches across. It's not very impressive-sounding, but suddenly becomes more so when you find out it's a single-celled organism.
  • Livyatan melvillei is a prehistoric sperm whale named after both the leviathan and Moby Dick via Melville. It earns the name by having the largest teeth of any known organism. It ate other whales and probably competed with Megalodons. Yikes.
  • Several species of pliosaur, including the so-called Predator X, were roughly whale-sized, but with jaws more resembling those of an alligator.
  • Praya dubia, or the Giant Siphonophore, is probably the closest thing to a real-life Lovecraftian undersea horror. Alien in appearance, it can be as long as 50 meters and lives at depths of up to a thousand meters. Fortunately, it's totally harmless and only about as thick as a broomstick.
  • Several deep sea fish are very bizarre and monstrous in appearance, with huge jaws filled with hundreds of needle-like teeth. Fortunately they tend to be very small compared to humans.
  • The very first one in history was the 600-million-year-old Anomalocaris, frequently dubbed the world's first apex predator. It was only about a meter long, but in comparison to the other creatures of the period, that's Kaiju-sized. Some of its relatives were pretty big too, like the filter-feeding Aegirocassis, which was 2 meters long.
  • Research done in 2014 revealed that Stock Dinosaur Spinosaurus was likely a freshwater variant on this trope, using short, ducklike hind limbs to paddle its way through rivers and eating large fish out of the water with its long crocodile-like jaws. For reference, Spinosaurus itself was sixty feet long, and its prey would have included fish as big as or bigger than grown humans. Later, in 2020, a mostly-complete Spinosaurus tail was discovered for the first time, which resembled an eel's tail, confirming the aquatic hypothesis and indicating Spinosaurus likely spent almost all of its life in the water.
  • The Walrus was often lumped in with sea monsters. Because very few people had actually seen one, their depictions in the late medieval and early modern period often barely resembled the real thing.

Alternative Title(s): Giant Swimmer


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